1. Field of the Invention
The present invention relates to a system for sensing a vibration displacement caused by a material in a medium by means of using a piezoelectric substrate, an interdigital arrangement of two comb-shaped electrodes formed on an upper end surface of the piezoelectric substrate, a counter electrode formed on a lower end surface of the piezoelectric substrate, and a signal analyzer.
2. Description of the Prior Art
Conventional devices for sensing a vibration displacement are classified into two types. One is touch-type, and the other is untouch-type. Devices as an electric micrometer for measuring a minute displacement, a linear scale for a large displacement, and a rotary encoder for a rotation displacement belong to the touch-type. The electric micrometer and the linear scale are popularly used as a reference for measuring the length of a material. The rotary encoder is used for controlling a rotation velocity or a rotation frequency of a rotatory material. The touch-type has some problems on measurement accuracy, response time, and has difficulties in use, durability and manufacturing. On the other hand, devices as a laser-type sensor and an electroacoustic-type sensor belong to the untouch-type. The laser-type sensor is mainly used for measuring a vibration displacement along the direction vertical to the laser beam applied to a material, and has a defect that the longer the length of the laser beam, the lower the measurement accuracy. In addition, it is impossible for the laser-type sensor to operate in opaque media. The electroacoustic-type sensor is easy to be affected by a change in circumstances, and has some problems on measurement accuracy.
An object of the present invention is to provide a vibration displacement sensing system capable of making an interdigital transducer act as a thickness mode transducer.
Another object of the present invention is to provide a vibration displacement sensing system operating with a quick response.
Another object of the present invention is to provide a vibration displacement sensing system need not a circulator, and so on.
Another object of the present invention is to provide a vibration displacement sensing system capable of making the radiation angle vertical.
Another object of the present invention is to provide a vibration displacement sensing system capable of low electric power consumption.
Another object of the present invention is to provide a vibration displacement sensing system capable of measuring the sound velocity in cellular tissue.
Another object of the present invention is to provide a vibration displacement sensing system excellent in durability and manufacturing.
Another object of the present invention is to provide a vibration displacement sensing system, which is not affected by a change in circumstances, for example, a change in temperature.
A still other object of the present invention is to provide a vibration displacement sensing system easy in use and having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is a vibration displacement sensing system comprising a piezoelectric substrate, first- and second comb-shaped electrodes formed on an upper end surface of the piezoelectric substrate, a counter electrode formed on a lower end surface of the piezoelectric substrate, and a signal analyzer. The first- and second comb-shaped electrodes form an interdigital arrangement. The counter electrode is in contact with a medium having a material therein.
If input electric signals are applied between the first comb-shaped electrode and the counter electrode, longitudinal waves are radiated into the medium along the direction vertical to the lower end surface of the piezoelectric substrate. The longitudinal waves are reflected at the material. If the material vibrates in response to times Ti (i=1, 2, . . . , n), reflected longitudinal waves are detected between the second comb-shaped electrode and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n) in accordance with distances Zi (i=1, 2, . . . , n) corresponding with the times Ti, respectively. On the other hand, electrical coupled-signals from the input electric signals are also detected between the second comb-shaped electrode and the counter electrode. The electrical coupled-signals and the delayed electric signals Di interfere respectively with each other, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Disclosing a relationship between respective amplitudes of the interference signals Ri and the times Ti provides an amplitude change of the relationship. Thus, the vibration displacement caused by the material is estimated from the amplitude change of the relationship.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the ratio of the interdigital periodicity of the interdigital arrangement to the thickness of the piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the medium to the longitudinal wave velocity in the piezoelectric substrate.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein increasing the number of electrode-finger pairs in the interdigital arrangement makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the first comb-shaped electrode is constant.
According to another aspect of the present invention there is provided a piezoelectric substrate made of a piezoelectric ceramic plate, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the medium is a liquid matter.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the medium is a cellular tissue.
According to another aspect of the present invention there is provided a vibration displacement sensing system further comprising a polymer film, with which the lower end surface of the counter electrode is coated.
According to another aspect of the present invention there is provided a vibration displacement sensing system further comprising a silicone rubber, with which the lower end surface of the counter electrode is coated.
According to another aspect of the present invention there is provided a vibration displacement sensing system comprising a first piezoelectric substrate, a first interdigital arrangement of two comb-shaped electrodes formed on a lower end surface of the first piezoelectric substrate, a second piezoelectric substrate, a second interdigital arrangement of two comb-shaped electrodes formed on an upper end surface of the second piezoelectric substrate, a counter electrode cemented between the first- and second piezoelectric substrates, and a signal analyzer. A lower end surface of the first interdigital arrangement is in contact with a medium having a material therein.
If input electric signals are applied between one of the two comb-shaped electrodes in the first interdigital arrangement and the counter electrode, longitudinal waves are radiated into the medium along the direction vertical to the lower end surface of the first piezoelectric substrate. The longitudinal waves are reflected at the material. If the material vibrates in response to times Ti (i=1, 2, . . . , n), reflected longitudinal waves are detected between one of the two comb-shaped electrodes in the second interdigital arrangement and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n) in accordance with distances Zi (i=1, 2, . . . , n) corresponding with the times Ti, respectively. On the other hand, electrical coupled-signals from the input electric signals are also detected between the one of the two comb-shaped electrodes in the second interdigital arrangement and the counter electrode. The electrical coupled-signals and the delayed electric signals Di interfere respectively with each other, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Disclosing a relationship between respective amplitudes of the interference signals Ri and the times Ti provides an amplitude change of the relationship. Thus the vibration displacement caused by the material is estimated from the amplitude change of the relationship.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the electrode-finger direction of the second interdigital arrangement is orthogonal to that of the first interdigital arrangement.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the finger width in the one of the two comb-shaped electrodes in the first interdigital arrangement is wider than that in the other of the two comb-shaped electrodes in the first interdigital arrangement, and the finger width in the one of the two comb-shaped electrodes in the second interdigital arrangement is wider than that in the other of the two comb-shaped electrodes in the second interdigital arrangement.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the ratio of the interdigital periodicity of the first interdigital arrangement to the thickness of the first piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the medium to the longitudinal wave velocity in the first piezoelectric substrate.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein increasing the number of electrode-finger pairs in the first interdigital arrangement makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the one of the two comb-shaped electrodes in the first interdigital arrangement is constant.
According to another aspect of the present invention there is provided a vibration displacement sensing system comprising a first piezoelectric substrate, a first comb-shaped electrode formed on a lower end surface of the first piezoelectric substrate, a second piezoelectric substrate, a second comb-shaped electrode formed on an upper end surface of the second piezoelectric substrate, a counter electrode cemented between the first- and second piezoelectric substrates, and a signal analyzer. A lower end surface of the first comb-shaped electrode is in contact with a medium having a material therein.
If input electric signals are applied between the first comb-shaped electrode and the counter electrode, longitudinal waves are radiated into the medium along the direction vertical to the lower end surface of the first piezoelectric substrate. The longitudinal waves are reflected at the material. If the material vibrates in response to times Ti (i=1, 2, . . . , n), reflected longitudinal waves are detected between the second comb-shaped electrode and the counter electrode as delayed electric signals Di (i=1, 2, . . . , n) in accordance with distances Zi (i=1, 2, . . . , n) corresponding with the times Ti, respectively. On the other hand, electrical coupled-signals from the input electric signals are also detected between the second comb-shaped electrode and the counter electrode. The electrical coupled-signals and the delayed electric signals Di interfere respectively with each other, so that respective interference signals Ri (i=1, 2, . . . , n) occur. Disclosing a relationship between respective amplitudes of the interference signals Ri and the times Ti provides an amplitude change of the relationship. Thus, the vibration displacement caused by the material is estimated from the amplitude change of the relationship.
According to another aspect of the present invention there is provided a vibration displacement sensing system, wherein the electrode-finger direction of the second comb-shaped electrode is orthogonal to that of the first comb-shaped electrode.
According to other aspect of the present invention there is provided a vibration displacement sensing system, wherein the ratio of the interdigital periodicity of the first comb-shaped electrode to the thickness of the first piezoelectric substrate is smaller than four times the ratio of the longitudinal wave velocity in the medium to the longitudinal wave velocity in the first piezoelectric substrate.
According to a further aspect of the present invention there is provided a vibration displacement sensing system, wherein increasing the number of electrode-finger pairs in the first comb-shaped electrode makes the directionality of the longitudinal waves sharper under a condition that the total amount of all the finger-areas of the first comb-shaped electrode is constant.